Spin jump into the Zebetite so that Samus takes damage and begins to flash.

Spin jump again on the same spot.

Now do a regular jump forward, and Samus will pass through the Zebetite.

When the first Zebetite has been cleared, the next three will not spawn, and it is hence possible to continue directly to Mother Brain.

It is necessary that Samus has the Ice Beam to freeze the Rinka with, and that Screw Attack is disabled. The steps must also be carried out in quick succession.

Kejardon provides an explanation of the glitch:

[T]he trick works [...] because spinjumping onto the frozen Rinka will move Samus left a pixel, past the zebetite's collision box. Once you're there, you're technically inside the zebetite and free to move around in it. You need to be invincible, though, or otherwise the zebetite will hit Samus and push her back out. [1]